The present invention relates to a system for performing the calculation between PCM signals which carry digital signals representing a voice signal and/or a picture signal.
A voice signal and/or a picture signal is sometimes treated in the form of a digital signal, for instance, a PCM signal which is the abbreviation of Pulse Code Modulation signal. Those signals are subject to calculations like an addition, a subtraction, a multiplication and/or a division, in the cases of measurement of electric power, the signal processing in an echo canceller, the signal processing in a digital filter, and/or the addition of two signals in a conference telephone service.
PCM signals have inevitably quantizing noise, since they are generated by quantizing analog signals. When a linear quantization is performed, the resultant quantizing noise is constant, irrespective of the amplitude of the signal. However when the signal to be quantized is a voice signal, a non-linear quantization in which the quantization in which the quantizing step depends upon the amplitude of an analog signal is performed so that the quantizing noise is the smallest in the given number of bits of the digital signal.
Conventionally, when the calculation of that non-linear PCM signal is performed, the non-linear PCM signal is first converted to a linear PCM signal, and then, the calculation is performed for the converted linear PCM signals providing the linear result, and finally, that linear result is reconverted to a non-linear PCM signal.
However, that prior art has the disadvantages that the calculator must be large and the calculation speed is slow since the calculator must perform the conversion and reconversion between a non-linear PCM signal and a linear PCM signal, and generally speaking a linear PCM signal has more bit positions than that of a non-linear PCM signal.